Three electrode flow meter

ABSTRACT

An improved electromagnetic flow meter is provided which includes means for nulling out the transformer or quadrature electromotive force which is independent of fluid flow and which is in quadrature phase with the useful flow signal. This nulling is achieved by juxtaposing to one of the electrodes of the flow meter a pair of electrodes (instead of a single electrode as is standard practice). This electrode pair is connected to the end points of an external potentiometer, and the wiper is connected to one of the amplifier input terminals. By adjusting the wiper position, a zero signal may be obtained from the amplifier at zero flow. External circuitry may also be provided for a manual or servo controlled fine adjustment of the quadrature electromotive force compensation.

United States Patent [1 1 Biscar Feb. 20, 1973 THREE ELECTRODE FLOWMETER Inventor: Jean P. Biscar, Laramie, Wyo.

The Regents of the University of California, Berkeley, Calif.

Feb. 22, 1971 Assignee:

Filed:

App]. No.:

US. Cl ..73/194 EM, i28/2.05 F Int. Cl ..G01f 1/00, A6lb 5/02 Field ofSearch ..73/l94 EM; 128/2.05 F

[5 6] References Cited UNITED STATES PATENTS l/l970 Barefoot ..73/l94 EMUX 5/1967 Westersten ..73/ l94 EM 6/1969 Westersten ..73/1 94 EM PrimaryExaminer-Charles A. Ruehl Attorney-Jessup 8L Beecher [57] ABSTRACT Animproved electromagnetic flow meter is provided which includes means fornulling out the transformer or quadrature electromotive force which isindependent of fluid flow and which is in quadrature phase with theuseful flow signal. This nulling is achieved by juxtaposing to one ofthe electrodes of the flow meter a pair of electrodes (instead of asingle electrode as is standard practice). This electrode pair isconnected to the end points of an external potentiometer, and the wiperis connected to one of the amplifier input terminals. By adjusting thewiper position, a zero signal may be obtained from the amplifier at zeroflow. External circuitry may also be provided for a manual or servocontrolled fine adjustment of the quadrature electromotive forcecompensation.

4 Claims, 7 Drawing Figures PATENTEDFEBZOW 3.717. 031

SHEET 10F 2 f 2 L3 I i F1 g. 2O

f El v v E2 2| F I g. 24 I7 Fig. 2B Fig.- 2C

MIXER [RESISTOR 1 BALANCING POTENTIOMETER T F 1 R L R4 3 INVENTOR JEA/EI? B/SCA/P i v Fl g. 3 BY 3 FLOW SIGNAL MW, (To AMPLIFIER) T ATTORNEYSPATEmmraszoma sum 2 or 2 Arrvanoyy;

THREE ELECTRODE FLOW METER BACKGROUND OF THE INVENTION The volume rateof blood flow can be determined quantitatively by an electromagneticflow meter applied externally to a blood vessel. Such an application,however, requires surgical exposure of the blood vessel and ofteninvolves extensive surgery. This is clearly undesirable, if routine useis to be made of electromagnetic flow meters for clinical measurement ofblood flow in patients.

In order to overcome the limitations of the prior art electromagneticflow meters, catheter type electromagnetic flow meters have beendeveloped which comprise an electromagnetic flow transducer incorporatedinto a thin flexible catheter type tube, and which may be insertedthrough a branch vessel, such as the femoral artery or jugular vein, andfrom where it may be maneuvered into a major artery, such as the aortaor pulmonary artery, or vein, such as the vena cava. C. J. Mills, Phys.Med. Biol. 11, 323, (1966) As is well known, the usual prior artelectromagnetic flow meter includes appropriate means for producing amagnetic field across the path of the moving liquid,

such as the blood in the blood vessel, so that the liquid is caused togenerate a voltage as it moves through the magnetic field, with thevoltage being directly proportional to the velocity of the liquid. Theelectrodes, which are displaced on opposite sides of the conduitcarrying the liquid, such as the blood vessel, develop a signal which isrepresentative of the liquid flow velocity, and which shall bedesignated herein as the flow signal.

However, as is well known, a quadrature voltage is also developed inmost electromagnetic flow meters of the type under consideration. Thisquadrature voltage has no relation to the fluid flow in the bloodvessel, and it has a tendency to cause errors in the resulting mea'surements of the fluid flow. In the past, somewhat elaborate phasesensitive detector means have been provided in an attempt to detect theflow signal independently of the aforesaid quadrature voltage.

The present invention is essentially a modification of the systemdescribed by A. Kolin in Proc. Natl. Ac. of Sc., Vol 63, No. 2, pp357-363, June 1969. It utilizes the same basic structure of a resilient,collapsible frame, but differs in providing an alternate to the method,shown on page 362 of the aforesaid reference, for nulling out undesiredquadrature EMFs.

The electromagnetic flow meter of the present invention includes anadditional (third) electrode, and circuitry is connected to theadditional electrode in which the quadrature voltage may be cancelled,as mentioned above, by an adjustment of electronic, magnetic orelectrical means, such as external adjustment circuitry for fineadjustment. The external circuitry may be manually or automaticallycontrolled to bring the resultant transfer voltage essentially to .zero,and to maintain, the transfer voltage at the zero level.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationof an electromagnetic intraluminal flow meter pick up or sensorconstructed in accordance with the concepts of the invention;

FIG. 2,'consisting of FIGS. 2A, 2B, and 2C, illustrates the orientationof the sensor in the flow conduit or lumen. FIG. 2A is a side elevation;FIG. 2B is a top plan; FIG. 2C is a cross section.

FIG. 3 is a fragmentary circuit diagram in which a balancingpotentiometer is used for balancing the quadrature voltages so as toderive a resultant zero quadrature voltage, and also including aresistance type mixer across which the flow signal is achieved;

FIG. 4 is a fragmentary circuit diagram like FIG. 3, but which includesmagnetic rather than resistance means as the mixer; and

FIG. 5 is a schematic diagram partly in circuit detail and partly inblock form showing an external servo control for automaticallymaintaining the aforesaid quadrature voltage at a zero resultant state.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT The electromagneticflow meter of the invention as shown in FIG. 1 includes a transducer orsensor portion, which may, for example, be in the form of a resilientwire-like loop frame 17, like the above mentioned Kolin system. The endsof the resilient frame 17 are welded or otherwise affixed to a feedertube 18.

Three electrodes E E and E are attached to the frame 17, and electricalcontact may be made to these electrodes by separate leads L L and Lconnected thereto. The leads L L and L extend through the tube 18. Theelectrodes E and E are mounted on the frame 17 to be disposed on oneside of the fluid flowing through the lumen or conduit 20, for example,and the electrode E is mounted on the opposite side of the frame 17 tobe disposed on the other side of the fluid flow 21 in the conduit. Anexternal magnetic means 58 (FIGS. 2A and 5) may be provided for creatingthe required magnetic field M within the conduit. A new approach toelectromagnetic blood flow determination by means of catheter in anexternal magnetic field." by Alexander Kolin, Proc. Natl. Ac. Sci., Vol.65, pp

52l-527, March 1970. Also note A. Kolin, Proc. Natl.

Ac. ofSci., Vol 63, No. 2 pp 357-363, June 1969.

The flow of fluid in the conduit through the magnetic field causes anelectromotive force to be developed, and this electromotive force isdetected by the potential difference between the electrodes E and E andalso by the potential difference between the electrodes E and E It isusual for the magnetic field to be made alternating, so that theresulting flow signals appearing across the electrodes E and E, and Eand E, are likewise alternating.

In the embodiment of FIG. 1, the leads L L and L, are broughtexternally, so that they may be connected into appropriate electriccircuits, which will be described. These circuits include, for example,balanc ing impedances across which the aforesaid quadrature voltagesappear in opposite phase and are cancelled, and the resulting flowsignals may appear across a mixing impedance or load.

The resilient frame 17 may take any appropriate shape, for example, itmay be circular as shown in FIGS. 1 and 2 or lens shaped as in theaforementioned Kolin system.

The leads L L and L in the embodiment of FIG. 1 are connected to thecircuit shown in FIG. 3. The circuit of FIG. 3 includes a balancingpotentiometer R, connected to the leads L L whereas the flow signal istaken across the terminals E-F, connected respectively to the lead L andto the movable contact of the potentiometer. The mixer resistor R thusconstitutes the load on the circuit, and the output is taken betweenpoint E which may for example be grounded, and point F, which preferablyis led to an amplifier. The potentiometer may be adjusted by anyappropriate means, either electronic or mechanical, in order to providea balance between the oppositely phased quadrature voltages. The flowsignal thus appears across the mixer resistor R The circuit of FIG. 3has been used in a constructed embodiment of the invention in which, forexample, the balancing potentiometer R had a resistance to 50 ohms, andthe mixer resistor R had a resistance of kilohms. The circuit of FIG. 3was used in conjunction with the instrument shown in FIG. 1 in theconstructed embodiment, in which a quadrature electromotive force of theorder of 1.5 millivolts was developed. This quadrature electromotiveforce was reduced, in accordance with known techniques, by physicaladjustment of the common electrode E down to a level of the order of -50microvolts. Then, by additional balancing thru adjustment of thepotentiometer R the quadrature electromotive force was compensated to alevel below l microvolt.

As shown in the embodiment of FIG. 4, the mixer resistor'R may bereplaced by a transformer T, the transformer including primary windingsrespectively included in the circuit between ,the potentiometer R, andthe respective leads L and L,. The flow signal is derived across thesecondary of the transformer T, that is, across the terminals E and F.

It will be appreciated that although resistance mixing means is used inthe circuit of FIG. 3, and inductive mixing means is used in the circuitof FIG. 4, the flow signal mixing may occur in the load itself, and maytake the form, for example, of an appropriate electronic circult.

The circuit of FIG. 3 is shown as being manually adjustable. However,the .circuit may be included in a control system, such as the system ofFIG. 5, so that appropriate, servo means may be used to maintain thecompensated quadrature voltage at a minimum level. In the system of FIG.5, for example, the flow signal is amplified in an amplifier 50, and theresultingamplified flow signal is detected in a phase detector 52.

The phase detector 52 is excited, for example, by a reference signalderived across a reference signal pickup coil 54 and shifted 90 by aphase shifter circuit 56.

The pick-up coil 54 is inductively coupled, for examappropriate servosystem 64. The servo s stem 64 contro s t e movable tap of thepotenttome er R and always tends to move that tap to a position suchthat the residual quadrature EMF from the amplifier 50 is maintained ata minimum level.

An improved electromagnetic flow meter is provided, therefore, which isconstructed so that the quadrature EMF is self-compensated within theinstrument itself, and which mayinclude further electrical or electroniccircuitry for providing a control, either manual or automatic, to reducethe quadrature EMF essentially to zero, and to maintain the quadratureEMF essentially at the zero level.

It will be appreciated that while particular embodiments of theinvention have been shown and described, modifications may be made. Itis intended to cover all such modifications which come within the scopeof the invention in the following claims.

What is claimed is:

1. A self-compensating sensor for an electromagnetic flow meter to belocated in a conduit to measure fluid flow therein; comprising:

frame means locatable in said conduit;

a common electrode mounted on one side of said frame means;

a pair of electrodes mounted on the other side of said frame meansacross said conduit from said com-' mon electrode; V

external circuit means including a first conductor extending around saidframe to said common electrode and connected thereto, a pair ofconductors extending around said frame to respective ones of said pairof electrodes and respectively connected thereto, a balancingpotentiometer connected across said pair of conductors, and signal mixermeans connected between said first conductor and a movable tap on saidpotentiometer, whereby said sensor develops a flow signal between eachof said pair of electrodes and said common electrode which is sensed bysaid signal mixer means, and also develops a pair of oppositely phasedelectromotive forces between said common electrode and respective onesof said pair of electrodes which are balanced out by adjustment of saidmovable tap on said balancing potentiometer.

2. The combination. defined in claim 1, in which said signal mixer meanscomprises a resistor.

3. The combination defined in claim 1, in which said signal mixer meanscomprises a transformer.

4. The combination defined in claim 1, and which includes servo controlmeans mechanically connected to the aforesaid movable tap on saidpotentiometer to maintain said tap in a position resulting inessentially zero quadrature electromotive force across saidsignal Imixermeans.

t a: a a: a

1. A self-compensating sensor for an electromagnetic flow meter to belocated in a conduit to measure fluid flow therein; comprising: framemeans locatable in said conduit; a common electrode mounted on one sideof said frame means; a pair of electrodes mounted on the other side ofsaid frame means across said conduit from said common electrode;external circuit means including a first conductor extending around saidframe to said common electrode and connected thereto, a pair ofconductors extending around said frame to respective ones of said pairof electrodes and respectively connected thereto, a balancingpotentiometer connected across said pair of conductors, and signal mixermeans connected between said first conductor and a movable tap on saidpotentiometer, whereby said sensor develops a flow signal between eachof said pair of electrodes and said common electrode which is sensed bysaid signal mixer means, and also develops a pair of oppositely phasedelectromotive forces between said common electrode and respective onesof said pair of electrodes which are balanced out by adjustment of saidmovable tap on said balancing potentiometer.
 1. A self-compensatingsensor for an electromagnetic flow meter to be located in a conduit tomeasure fluid flow therein; comprising: frame means locatable in saidconduit; a common electrode mounted on one side of said frame means; apair of electrodes mounted on the other side of said frame means acrosssaid conduit from said common electrode; external circuit meansincluding a first conductor extending around said frame to said commonelectrode and connected thereto, a pair of conductors extending aroundsaid frame to respective ones of said pair of electrodes andrespectively connected thereto, a balancing potentiometer connectedacross said pair of conductors, and signal mixer means connected betweensaid first conductor and a movable tap on said potentiometer, wherebysaid sensor develops a flow signal between each of said pair ofelectrodes and said common electrode which is sensed by said signalmixer means, and also develops a pair of oppositely phased electromotiveforces between said common electrode and respective ones of said pair ofelectrodes which are balanced out by adjustment of said movable tap onsaid balancing potentiometer.
 2. The combination defined in claim 1, inwhich said signal mixer means comprises a resistor.
 3. The combinationdefined in claim 1, in which said signal mixer means comprises atransformer.